Building Instructions

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Connect the light sensor wire to port 3 on the
NXT. Insert the pegs into the correct holes as shown below, then
adjust the axles until the light sensor sits flat against the beams on
the sides of the channel.

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This step builds the conveyer pusher and the
calibration stick, which are loose parts that are not attached to the
sorter machine.

The conveyor pusher will be placed behind the pegs on
the conveyor, as shown below.

The calibration stick is used to calibrate the light
sensor. See "Using the Peg Sorter" below.

Peg
Sorter Programming

Use the Peg_Sorter
program for the Peg Sorter. You will also need the
Calibrate_L3 program to
calibrate the light sensor beforehand.

Important: See the instructions below to calibrate
and properly set up the Peg Sorter.

Using the Peg Sorter

Before using the Peg
Sorter, the light sensor must be calibrated. You can use the
Calibrate_L3 program to
calibrate the light sensor, which has two steps as shown below.
You only need to calibrate the light sensor once after building the
model. The calibration will be remembered after that.

When the calibration program tells you to center the sensor
over the black color, insert the calibration stick so that
the black axle is completely under the light sensor and
centered and flat on the bottom of the channel.

When the calibration program tells you to put the sensor
over white, remove the calibration stick so that the sensor
sees the white beam at the bottom of the channel.

Use the knob on the
side of the conveyor motor to move the conveyor stick back to make
room for the conveyor pusher and the pegs, and load the pegs into
the conveyor, as shown below. The pegs will push better if you
alternate the pegs with the long and short side first down, then up,
then down, etc. Also, to get good sorting results, do not put
two black pegs in a row anywhere in the sequence.

Important: As currently
designed, the Peg Sorter works best if there are not two
black pegs in a row anywhere in the sequence. This
is because the mechanical hitter cannot recover fast
enough after hitting one black peg to get the next one
right afterwards.

Make sure the hitter
bar (which has two small black gears on either side) starts out
horizontal, as shown below. Turn it with your hand as
necessary before starting the program.

Make sure the hitter
bar starts out horizontal.

Run the
Peg_Sorter program. If the black pegs are not being hit at
the right time (if you think the hitter is swinging slightly too
early or too late), you can try adjusting the hitting delay by using
the left and right arrow buttons on the NXT.

The delay time between
when the light sensor sees a black peg to when the
hitter starts its motion is displayed on the NXT screen
and can be adjusted with the left and right arrow
buttons on the NXT.

Challenges

A goal for real
mechanical sorters in factories is to sort items as quickly as
possible. See if you can make any improvements to the sorter
to allow it to sort faster. To get the program to run the
conveyor faster, you just need to increase the power level on the
Motor block that is controlling the conveyor (Motor C), but if you
run it faster it might start to miss black pegs. At the
designed speed, it can sort well as long as the black pegs don't
come any faster than every other peg. If the black pegs are
spaced even farther apart, it could sort even faster without any
other changes, but a challenge would be to get it to sort faster
while still allowing more black pegs. One idea for an
improvement would be to redesign the hitting arm to start closer to
the pegs and not need to swing as far. This would allow it to
recover faster. For example, perhaps make a hitter with four
arms instead of two, and don't gear the hitting motor up as much.

Try modifying the
conveyor to allow for more pegs to fit into it.

Of course this Peg
Sorter is not really a practical way to actually sort your NXT pegs.
Aside from using most of the parts in your NXT set, it takes way too
long to load the pegs into the conveyer. Could you design a
way to just dump the pegs into a bin and then have the machine feed
them into the channel somehow?

The sorter could be
fairly easily modified to sort normal sized pegs instead of the long
pegs, so you could try that. This would also open up a
possibility for an advanced challenge: try to sort three different
colors of pegs. For example, gray pegs fall straight through,
black pegs are hit to the left, and blue pegs are hit to the right.
This will require changing the program to sense three levels of
brightness, so it will get more complex then just "wait for dark
enough, then hit" in the program.